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Average Speed Question

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Average Speed Question

by hijazim » Sun Mar 01, 2009 1:41 am
Image

Clearly the answer should be = 70miles/2h = 35 miles/h
So the nearest is 35.5 which is answer D.
The right answer in the book is 34.3 which is C

Any suggestions why??
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by deepoe » Sun Mar 01, 2009 1:55 am
Assume he drove 30 miles in 1 hour ( 30 m/h )

Than he drove the 30 miles with a speed of 40 m/h.

30 / 40 = 0,75 H

1,75 H he took for both drives.


60 / 1,75 = 34,3
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by hijazim » Sun Mar 01, 2009 3:03 am
Thx man.. It's really not that hard.. but the approach is the thing.. thx again
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by deepoe » Sun Mar 01, 2009 3:09 am
hijazim wrote:Thx man.. It's really not that hard.. but the approach is the thing.. thx again
Jep I got that problem too with some of the GMAT questions hehe :D
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by bhavikrao » Sun Mar 01, 2009 5:53 pm
folks,

If you the same distance but different speeds, the formula is

2ab/a+b

= 2*30*40/30+40

and you will get the answer
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by krisraam » Sun Mar 01, 2009 7:44 pm
deepoe wrote:Assume he drove 30 miles in 1 hour ( 30 m/h )

Than he drove the 30 miles with a speed of 40 m/h.

30 / 40 = 0,75 H

1,75 H he took for both drives.


60 / 1,75 = 34,3
When assuming values assume the values in such a way that we don't run into decimals.

Usually the LCM of the values

Here 30 and 40 are the numbers.

Assume he traveled 120 miles instead of 30.

Thanks
raama
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